Introduction:
This experiment was designed to carry out to completion the acid catalyzed dehydration of cyclohexene from cyclohexanol. Within organic chemistry, elimination reactions fall under that broad category of transformations. There are two types of elimination reactions, E1 and E2. This experiment dealt with an E1 reaction. The E1 reactions are most mechanically (we chemists say "mechanistically") similar to SN1 reactions, but also compete with both types of substitution reactions. E1 reactions are two step reactions. In order for an E1 reaction to take place, the reagents must be either a poor nucleophile or a weak base, and an electrophile. If the leaving group attached to the electrophile happens to be an OH group it must be pronated by a strong acid in order to form a more acceptable leaving group. With the absence of the leaving group, an intermediate carbocation is formed. The original pronation of the OH group also spurs the formation of a weak base, which is able to pluck a beta hydrogen from the electrophile. The end result is the formation of an alkene between the carbon to which the leaving group was attached to and the remaining hydrogen. It is also important to mention that elimination reactions only occur when heat is involved. Using Infrared Spectroscopy the success of distillation and the purity of the product was measured.Careful! You are lapsing here into a retrospective account of what happened....save that for your Conclusion. Infrared spectroscopy allows certain characteristics of a molecule to be seen based on comparison of the frequencies of the bonds within the molecule and and frequencies of the absorbed radiation. The infrared spectroscopy of the product was compared with a different spectroscopy done of a sample of cyclohexene.
Cyclohexanol Cyclohexene
Your images are not coming through for me. I'll see later if I can view them from the PC in my office (I'm on the Mac laptop at home right now), but I haven't encountered this problem with other reports. Can you all see the images from each of your computers? Data:
The temperature graph begins at 0; but, the actual elapsed time to 0 was 58 minutes where the temperature held steady at 27 C. The 0 mark beginning of the graph indicates the time when the condensation (vapor is perhaps the word to use here) made it to the top of the aparatus and the temperature began to rise.
Infrared Spectroscopy
The top graph is the graph from our teams experiment. The slight dip under the title "terrycyclohexene" is an indication that H2O (H-O-H) is present in the sample. By comparing our graph with another teams graph, "tomcyclohexene" below, we see that the top sample had less H2O and was therefore more pure. It is also interesting to note the spike at approximately 2400 has grown, nearly doubling from the time of the first graph below "tomcyclohexene" to the time of the top graph "terrycyclohexene". According to Dr. Higginbotham, this spike represents CO2 (O=C=O)and was present in the sample due to the exhalation from just a few individuals in the room.
:
Analysis:
Theoretical yield: in the equation the phosphoric acid is acting as the catalyst.
Theoretically 0.074 moles(7.411g) of cyclohexanol should produce 0.074 moles of cyclohexene, cyclohexene by multiplying the MW of cyclohexene (82.1 g/mol). 0.074 mol x 82.1 g/mol = 6.075 g of cyclohexene
In other words, 7.411g of cyclohexanol should produce 6.075 g of cyclohexene, known as the theoretical yield. yep. good on this calculation.
3,368 grams of Cyclohexene (experimental yield)x 100 = 55.4 % yield recoveredYou've got one more sig fig in this calculation. 6.075 grams of Cyclohexene (theoretical yield)
Conclusion:
The IR spectrum in the graph above shows a cyclohexene as one of the products. The elimination reaction E1 of an alcohol includes the loss of an OH from the carbon and the loss of an H from an adjacent beta carbon. Because the OH group is a very poor leaving group, an alcohol is able to undergo dehydration only if its OH group is converted into a better leaving group. One way to convert the OH group into a good Leaving group is to protonate it. In the first step of the dehydration reaction, protonation changes the very poor leaving group –OH into a good leaving group –OH2+.The resulting product is an alkene (pi-bond) and a molecule of water.
In most cases, an E1 reactions with an OH requires an acid catalyst and heat. In the experiment Phosphoric acid was used, one the most common acid catalysts. When more than one elimination product can be formed, the major product is the more substituted alkene. This is achieved by removing a proton from the adjacent carbon that has fewer hydrogens, this is known as Zaitsev’s rule. The more substituted alkene is the major product because it is the more stable alkene, it has the more stable transition state leading to its formation.
The fact that the CO2 spike grew so much, in such a short time, and absorbs infrared energy so well, is a testament to the real threat it poses as it continues to increase in our atmosphere. *Here is a graph of a cyclohexene for comparison purposes (graph from http://orgchem.colorado.edu/)
Post Lab Question: Atom economy: the mass of the desired product divided by the mass of all reactants
Atom economy: .99 x 100 = 99%Since water is not a desired (valuable) product, your calculation should not include it. So it's 82.14/100.58. Does this make sense?
I really can not evaluate this report without the missing data. I am recording a 6.5 for you, and hope that you can solve the problems in time to turn it back in as your "7th inning stretch" report.
UPDATE 2/23 This lab earned the following scores for: format (2/2) style (1.5/2) data (3/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (1/2) error (0/1) post-lab Q (1.5/2) for a total of 10.5/14. The conclusion could be improved by changing the focus from a general discussion of this reaction type to a discussion of your particular results, and how they provide evidence for the ideas about cyclohexanol you have learned in class.
Introduction:
This experiment was designed to carry out to completion the acid catalyzed dehydration of cyclohexene from cyclohexanol. Within organic chemistry, elimination reactions fall under that broad category of transformations. There are two types of elimination reactions, E1 and E2. This experiment dealt with an E1 reaction. The E1 reactions are most mechanically (we chemists say "mechanistically") similar to SN1 reactions, but also compete with both types of substitution reactions. E1 reactions are two step reactions. In order for an E1 reaction to take place, the reagents must be either a poor nucleophile or a weak base, and an electrophile. If the leaving group attached to the electrophile happens to be an OH group it must be pronated by a strong acid in order to form a more acceptable leaving group. With the absence of the leaving group, an intermediate carbocation is formed. The original pronation of the OH group also spurs the formation of a weak base, which is able to pluck a beta hydrogen from the electrophile. The end result is the formation of an alkene between the carbon to which the leaving group was attached to and the remaining hydrogen. It is also important to mention that elimination reactions only occur when heat is involved. Using Infrared Spectroscopy the success of distillation and the purity of the product was measured.Careful! You are lapsing here into a retrospective account of what happened....save that for your Conclusion. Infrared spectroscopy allows certain characteristics of a molecule to be seen based on comparison of the frequencies of the bonds within the molecule and and frequencies of the absorbed radiation. The infrared spectroscopy of the product was compared with a different spectroscopy done of a sample of cyclohexene.
Your images are not coming through for me. I'll see later if I can view them from the PC in my office (I'm on the Mac laptop at home right now), but I haven't encountered this problem with other reports. Can you all see the images from each of your computers?
Data:
The temperature graph begins at 0; but, the actual elapsed time to 0 was 58 minutes where the temperature held steady at 27 C. The 0 mark beginning of the graph indicates the time when the condensation (vapor is perhaps the word to use here) made it to the top of the aparatus and the temperature began to rise.
Infrared Spectroscopy
The top graph is the graph from our teams experiment. The slight dip under the title "terrycyclohexene" is an indication that H2O (H-O-H) is present in the sample. By comparing our graph with another teams graph, "tomcyclohexene" below, we see that the top sample had less H2O and was therefore more pure. It is also interesting to note the spike at approximately 2400 has grown, nearly doubling from the time of the first graph below "tomcyclohexene" to the time of the top graph "terrycyclohexene". According to Dr. Higginbotham, this spike represents CO2 (O=C=O)and was present in the sample due to the exhalation from just a few individuals in the room.
:
Analysis:
Theoretical yield: in the equation the phosphoric acid is acting as the catalyst.
Theoretically 0.074 moles(7.411g) of cyclohexanol should produce 0.074 moles of cyclohexene, cyclohexene by multiplying the MW of cyclohexene (82.1 g/mol).
0.074 mol x 82.1 g/mol = 6.075 g of cyclohexene
In other words, 7.411g of cyclohexanol should produce 6.075 g of cyclohexene, known as the theoretical yield. yep. good on this calculation.
3,368 grams of Cyclohexene (experimental yield) x 100 = 55.4 % yield recovered You've got one more sig fig in this calculation.
6.075 grams of Cyclohexene (theoretical yield)
Conclusion:
The IR spectrum in the graph above shows
In most cases, an E1 reactions with an OH requires an acid catalyst and heat. In the experiment Phosphoric acid was used, one the most common acid catalysts. When more than one elimination product can be formed, the major product is the more substituted alkene. This is achieved by removing a proton from the adjacent carbon that has fewer hydrogens, this is known as Zaitsev’s rule. The more substituted alkene is the major product because it is the more stable alkene, it has the more stable transition state leading to its formation.
The fact that the CO2 spike grew so much, in such a short time, and absorbs infrared energy so well, is a testament to the real threat it poses as it continues to increase in our atmosphere. *Here is a graph of a cyclohexene for comparison purposes (graph from http://orgchem.colorado.edu/)
Post Lab Question:
Atom economy: the mass of the desired product divided by the mass of all reactants
Cyclohexanol: Molecular Formula-C6H12O, Molecular Weight-100.58g/mol
Cyclohexene: Molecular Formula-C6H10, Molecular Weight-82.14g/mol and H20-18.053=100.193g/mol
Atom economy: .99 x 100 = 99% Since water is not a desired (valuable) product, your calculation should not include it. So it's 82.14/100.58. Does this make sense?
I really can not evaluate this report without the missing data. I am recording a 6.5 for you, and hope that you can solve the problems in time to turn it back in as your "7th inning stretch" report.
UPDATE 2/23
This lab earned the following scores for: format (2/2) style (1.5/2) data (3/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (1/2) error (0/1) post-lab Q (1.5/2) for a total of 10.5/14. The conclusion could be improved by changing the focus from a general discussion of this reaction type to a discussion of your particular results, and how they provide evidence for the ideas about cyclohexanol you have learned in class.